The present invention relates to the structure of diamonds which are used in a so-called "diamond anvil".
A diamond anvil is an apparatus which allows direct viewing or monitoring of a material that is highly compressed between two surfaces. Scientific American, Vol. 250 (April, 1984) pp. 54-62. Diamond anvil apparatus includes a pair of circularly shaped diamonds coaxially arranged with facing, plane parallel bearing surfaces and a device for applying a force to these diamonds tending to press the bearing surfaces together. Pressures higher than those at the center of the earth have been achieved with this apparatus.
The diamond anvil has been developed from the so-called "Bridgeman anvil", circa 1905, which used tungsten carbide for one or both of the pressure producing surfaces and was opaque to visible wavelength radiation. In 1959, Weir, Lippincott, Van Valkenberg and Bunting, of the National Bureau of Standards and, independently, Jamieson, Lawson and Nachtrieb of the University of Chicago, fabricated the first diamond anvils for high pressure materials investigation. Conventionally, diamond anvil apparatus has employed circularly shaped, brilliant cut diamonds arranged coaxially with their top or bottom facets facing each other and serving as the bearing surfaces that apply a force to the test material. This force tending to press the bearing surfaces together which may be generated by a hydraulic press or a screw device, etc., is applied in the axial direction to the opposite facing surfaces of the two diamonds.
In order to prevent the test material from being squeezed out of the space between bearing surfaces, a malleable gasket is arranged between the two diamonds. This gasket has a central opening for the test material and comes in contact with the edges of the bearing surfaces on opposite sides. When the bearing surfaces of the two diamonds are pressed toward each other, the gasket is compressed permitting the diamonds to approach each other and apply a force to the test material.
Due to enormous and often unequal forces generated during a test, the sharp edges of the bearing surfaces tend to fracture or crack. Such fractures, when they occur, prevent the even application of force to the test material.
Efforts have been made to reduce the fragility of the diamond edges by providing one or more rows of bevels adjacent to the bearing surface edges so that included angles are not as sharp. See U.S. Pat. No. 4,776,223. However, even this configuration has angular edges which are relatively fragile.